Lab quiz 3 ex. 9

Questions and Answers

What is the primary function of agar in a culture medium?

To act as a solidifying agent, allowing the medium to solidify at a temperature below its melting point.

What is the minimum temperature required to melt agar and put it into solution?

100°C (boiling)

What is the purpose of sterilization in microbiological culture preparation?

To completely remove or destroy all living cells, viable spores, and viruses from a medium or object.

What are the standard conditions for autoclave sterilization of culture media?

121°C at a pressure of 15 pounds per square inch (psi) for 15 minutes. Signup and view all the answers

What is the primary component of glucose-tryptone-yeast extract (GTYE) medium that provides a source of amino acids?

Tryptone, which is a mixture of peptides and amino acids obtained through partial digestion or hydrolysis of casein. Signup and view all the answers

What is the purpose of adding potassium phosphate to GTYE medium?

To stabilize the pH of the medium as a buffer. Signup and view all the answers

At what temperature is the GTYE medium cooled to before pouring into plates?

Approximately 56°C (just bearable when touched to the back of the wrist). Signup and view all the answers

What is the importance of using aseptic technique during the preparation of GTYE medium and pour plates?

To prevent contamination of the medium and plates with microorganisms from the environment. Signup and view all the answers

What are the essential chemical elements required by microorganisms for growth, and where do they obtain them from?

Microorganisms require the same chemical elements as higher forms of life, and they obtain them from their immediate environment. Signup and view all the answers

What are the four key components that a culture medium must provide to support microbial growth?

A suitable carbon source, a suitable nitrogen source, a source of energy, and stability of pH during growth. Signup and view all the answers

Distinguish between defined and complex culture media, highlighting their uses and limitations.

Defined media have known components, useful for studying microbial metabolism, while complex media have unknown ingredients, suitable for providing a rich and complete medium for many microorganisms. Signup and view all the answers

What is the purpose of a selective culture medium, and how does it differ from an enrichment medium?

A selective medium favors the growth of a particular microorganism, whereas an enrichment medium selects for the fastest-growing microorganisms in a population. Signup and view all the answers

How does a differential culture medium differ from other types of culture media, and what is its purpose?

A differential medium distinguishes between different groups of bacteria, allowing researchers to identify and characterize specific microbial populations. Signup and view all the answers

What determines the selectivity of an enrichment culture, and is it solely based on the chemical composition of the medium?

The selectivity of an enrichment culture is not determined solely by the chemical composition of the medium, but also by other factors such as temperature, pH, and incubation time. Signup and view all the answers

What is the significance of pH stability in a culture medium, and how is it achieved?

pH stability is critical for microbial growth, and it is achieved by using buffers that maintain a stable pH during incubation. Signup and view all the answers

Study Notes

Microorganisms' Nutritional Requirements

Microorganisms require the same chemical elements for growth as higher forms of life
Nutritional and environmental needs must be met for effective culture medium preparation

Types of Culture Media

Defined medium (synthetic medium): has known components, useful for studying metabolism of a microorganism
Complex medium (undefined medium): contains ingredients of unknown composition, useful for providing a rich and complete medium
General purpose medium: allows growth of many microorganisms
Enrichment medium: selects for microorganisms with the highest growth rate
Selective medium: favors growth of a particular organism
Differential medium: distinguishes between different groups of bacteria

Agar as a Solidifying Agent

Agar is a complex polysaccharide extracted from red algae
It is attacked by relatively few bacteria
Agar is melted at 100°C (boiling) and remains liquid until the temperature falls to about 44°C

Sterilization of Culture Media

Sterilization is the complete removal or destruction of all living cells, viable spores, and viruses from a medium or object
Physical agents such as heat, filtration, and radiation are commonly used for sterilization
Autoclave sterilization: uses saturated steam under high pressure, standard conditions are 121°C at 15 psi for 15 minutes

Preparation of Glucose-Tryptone-Yeast Extract (GTYE) Medium

GTYE medium supports growth of a wide variety of bacteria
Components include glucose, tryptone, yeast extract, and potassium phosphate in a buffered solution solidified with agar
Beef extract contains amino acids, peptides, nucleotides, organic acids, vitamins, and minerals
Tryptone is mainly a mixture of peptides and amino acids
Yeast extract is a source of B vitamins, nitrogen, and carbon compounds

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Description

This quiz covers the importance of culture media in meeting the nutritional requirements of microorganisms. It discusses the diversity of environmental components that provide essential elements for growth.